Question

Example 1: Find the square of the following numbers without actual multiplication.
(1) 39
ü) 42​

Answer 1

(i) 39 = 30+9

${(30 + 9)}^{2}$

$= {(30)}^{2} + 2.30.9 + {(9)}^{2}$

$= 900 + 540 + 81$

$= 1521$

(ii) 42=40 + 2

${(40 + 2)}^{2}$

$= {(40)}^{2} + 2.40.2 + {(2)}^{2}$

$= 1600 + 160 + 4$

$= 1764$

Answer 2

Answer:

39= 39*39 = (40-1)(40-1) = (40*40) - (-1* -1) -40 -40 = 1600 - 84 = 1521